An elderly woman sips water after being taken to hospital during a heatwave in Paris which claimed dozens of lives in 2003. Photograph: Franck Prevel/AP

The Heat-Health Watch system is now in operation in England in case the weather turns hot. Local authorities, the health service and anyone looking after children, elderly people and those who are otherwise vulnerable are supposed to swing into action if the forecast for daytime temperatures is 30C or above and 15C at night.

The danger threshold varies around the country depending on the "normal" temperatures people are used to. Those living in London, for example, are supposed to be able to withstand daytime temperatures of 32C and 18C at night. In northeast England, on the other hand, the trigger for action is 28C and 15C.

Problems can occur at lower temperatures, for example in the London tube. If temperatures exceed 24C for three days running, hot weather notices are put up and bottled water supplied. Work on preventing rails buckling also begins.

There has been a new updated plan every year since 2004 in response to a heatwave that occurred in the southeast in 2003, when 2,000 extra deaths were reported in a 10-day period in August. Since then, two more heatwaves have claimed lives: 680 people died in 2006 and 300 in 2009.

The key to survival for vulnerable groups is to avoid the sun around mid-day and to find some way of getting cool at night to prevent strain on the heart and other vital organs.

If a heatwave is expected, all weather forecasts will carry a warning and all the relevant authorities will be alerted. We can all relax on 15 September, when the Department of Health deems the danger passes for another year.